1. Field of the Invention
The present invention relates to a method of controlling the propelling direction of a shield tunneling machine used in the pipe-jacking process, and an apparatus therefor.
2. Description of the Prior Art
The semi-shield process is applied for laying a conduit for sewerage or service water, wherein a shield tunneling machine is arranged, and the shield tunneling machine and Hume pipes following the shield tunneling machine are propelled by a pipe-jacking machine. In the semi-shield process, laser beam is sent along a scheduled line on which a conduit is to be laid, the shield tunneling machine and a plurality of pipes are propelled along the laser beam by the pipe-jacking machine, while the ground is excavated by the shield tunneling machine.
When the shield tunneling machine is propelled, a variety of resistances are applied on the shield tunneling machine. Therefore, it happens that the propelling direction of the shield tunneling machine is deviated from the scheduled line. In order to control the propelling direction of the shield tunneling machine, the shield tunneling machine is provided with a target on which a laser beam is projected, with a television camera by which an image of the target is taken, and with a pointer wherein a forward end of the pointer is attached to a cutter head of the shield tunneling machine and a rear end of the pointer is disposed by the surface of the target.
An image of a laser spot projected on the target is taken by the television camera. The image of a laser spot projected on the target is projected on a Braun tube and observed by an operator. When it is checked the projecting direction of the shield tunneling machine is deviated from the scheduled line, a directional control means, that is, jacks are controlled so that the cutter head is turned against the tail shield by which the direction of the shield tunneling machine is adjusted according to the movement of the pointer which corresponds to the orientation of the cutter head and the tail shield and an angle between the cutter head and the tail shield.
In the shield tunneling machine, the target is mounted at a certain place in the shield tunneling machine. The shield tunneling machine is propelled by a pipe-jacking machine disposed in a start vertical shaft, while a laser beam is sent from a laser beam source disposed in the start vertical shaft to the target. A spot of laser beam projected along the scheduled line on the target is made the origin on the target, and when the spot on the target, while the shield tunneling machine is projected, is displaced from the origin to the another place, it is found only that the section of shield tunneling machine is displaced from the scheduled line corresponding to the position of the spot of laser beam projected on the target, from an image of Braun tube.
Accordingly, from the observation of a spot of laser beam on the target which is displaced from one origin to another origin, it is difficult to find a control amount of the directional control means. Therefore, at present, the directional control of shield tunneling machine demands skill of an operator and his know-how.
Recently, a shield tunneling machine was developed in which a laser beam is sent along a scheduled line to a target, which is pervious to light, and a laser beam passing through the target is reflected by a reflector. The reflected laser beam by the reflector is projected on a screen, and the advanced direction of the shield tunneling machine can be controlled by observing a spot of laser beam projected on the target and a spot of laser beam protected on the screen. In the shield tunneling machine, the displacement of the spot of laser beam projected on the screen, while the shield tunneling machine is advanced, from the original spot of a laser beam projected on the screen is detected by observing the screen, and the advanced direction of the shield tunneling machine is controlled corresponding to the detected displacement of spot of laser beam.